1. Technical Field
The present invention relates to a commutator motor provided with a commutator.
2. Background of Art
FIG. 9 is a sectional view of a conventionally used commutator motor. In FIG. 9, the commutator motor 10 is mainly comprised of a rotary shaft 1, an armature 2, a commutator 3, a brush holder 4, a brush 41, a brush casing 42, a magnet 5, a yoke 6, a bearing 7, and a housing 8. Further, the commutator 3 has a conductive section 32 mounted on the rotary shaft 1 through an insulating section 31 disposed between the conductive section 32 and the rotary shaft 1, the rotary shaft 1 is pressed into and held in the hole in the center of the insulating section 31, and the conductive section 32 is brought into contact with the brush 41.
In the structure of the commutator motor 10 constituted as above, when rotating the armature 2, vibration is generated in the contact portion between the brush 41 and the commutator 3. A hard material of a high mechanical strength, for example, thermosetting resin like thermoset phenolic resin, forms the insulating section 31 of the commutator 3. Thus, the insulating section 31 can securely hold the rotary shaft that is pressed into the insulating section 31. Since the commutator 3 behaves, due to the mentioned structure, as a rigid body as a whole, the vibration described above is directly transmitted to the rotary shaft 1 without attenuation in the commutator 3. The vibration is then transmitted to the bearing 7 incorporated in the rotary shaft 1 and further to the yoke 6. Such transmission of vibration is one of the causes of vibration and noise generated in the commutator motor 10. Furthermore, the torque of the commutator motor 10 is transmitted from the armature 2 to the output side and the torque thus transmitted in the commutator motor 10 gives rise to a torsional strain in the direction of rotation along the rotary shaft 1. This torsional strain brings about positional displacement in the direction of rotation between the commutator 3 and an armature core 21, and consequently the armature coil 22 is subjected to tensile stress. This stress is one of the causes responsible for coil breakage due to fatigue fracture.
The Japanese Utility Model Publication (examined) No. 21085/1995 has disclosed a technique of giving a floating support to a brush holder forming a part of a housing by using rubber bushes for end-brackets, for the purpose of absorbing vibration in radial and axial directions due rotation of an armature in a commutator motor. This known technique is, however, not always sufficient to prevent the mentioned vibration and noise of a commutator motor.
In view of the above-discussed problems incidental to the conventional commutator motor, it is an object of the present invention to reduce vibration and noise generated in commutator motor, and to improve durability against breakage of armature coil.
(1) A commutator motor according to the invention comprises: a commutator having a conductive section mounted on a rotary shaft through an insulating section between the conductive section and the rotary shaft; and a vibration-isolating member disposed between the conductive section and the rotary shaft.
(2) In the commutator motor according to the mentioned paragraph (1), the vibration-isolating member is formed on an inner surface of the insulating section, the inner surface facing the rotary shaft, by adhesion to or integral formation with the insulating section.
(3) In the commutator motor according to the mentioned paragraph (1), the vibration-isolating member is formed between the conductive section and the insulating section by adhesion to or integral formation with these two sections.
Accordingly, vibration developed in the contact portion between a brush and the commutator due to rotation of the armature, is absorbed by the vibration-isolating member prepared in various forms as described above, whereby the commutator motor is prevented from occurrence of vibration and noise generated. Furthermore, due to the absorption of vibration by the vibration-isolating member, the mentioned torsional strain does not occur, and consequently the problem associated with fatigue fracture of armature coil can be solved.
(4) In the commutator motor according to any of the above-mentioned paragraphs (1) to (3), the vibration-isolating member has protrusions embedded in the insulating section in a radial direction of the rotary shaft. Accordingly, the protrusions exhibit an advantage of preventing positional displacement of the vibration-isolating member in an axial direction with respect to the insulating section.
(5) In the commutator motor according to the mentioned paragraph (1), the commutator motor further comprises a brush holder section for holding a brush coming in contact with the commutator, and in which another vibration-isolating member supports the bush holder section. Accordingly, in addition to isolation of vibration by the vibration-isolating member disposed between the conductive section and the rotary shaft as described above, another way of preventing vibration is provided by another vibration-isolating member. As a result, the commutator motor is more securely prevented from occurrence of vibration and noise. Furthermore, any torsional strain along the rotary shaft does not occurs, whereby the problem associated with fatigue fracture of the armature coil is solved.
(6) In the commutator motor according to the mentioned paragraphs (1) or (5), the vibration-isolating member is made of rubber. Accordingly, excellent elasticity of rubber can provide a great vibration-isolating effect.